In production of an organic EL device, as a method for forming a thin film of an organic compound (hereinafter sometimes referred to as a material), a vacuum deposition method has been known. The vacuum deposition method is a method of forming a thin film by property combining an evaporation source and a substrate for deposition in a vacuum chamber, and has such an advantage that a homogeneous thin film is likely to be obtained as compared with a wet process such as a spin coat method or a dip method. As the vacuum deposition method, e.g. a resistance heating deposition method in which a material is made to adhere to a metal container (metal board) having a relatively high electrical resistance and an electric current is applied to the metal container, whereby the metal container is made to generate heat and the material is evaporated, to form a thin film of the material on the surface of a substrate for deposition, and an electron beam/laser beam deposition method in which a material is irradiated with an electron beam or a laser beam, whereby the material is evaporated by the energy of the beam to form a thin film of the material on the surface of a substrate for deposition, have been known. Particularly, the resistance heating deposition method is widely used since the structure of the deposition apparatus is simple, and formation of a high quality thin film can be realized at a low cost.
In the case of an apparatus used for the above deposition method, part of the evaporated material is deposited on the surface of a substrate for an organic EL device, and the remainder is accumulated on the inner surface of a chamber of the deposition apparatus or on the surface of components disposed in the chamber. Accordingly, the material to form the thin film on the surface of the substrate for an organic EL device is part of the entire material, and the most part adheres to e.g. the inner surface of the chamber and is wasted without being utilized. An expensive compound is used for the material of an organic EL device in many cases, and thus the production cost of the device tends to be high if the material cannot efficiently be used. Further, when the chamber is used for deposition of another material, the material accumulated on the inner surface of the chamber may be contained as an impurity in the film, whereby the film may be contaminated.
In order to overcome the above problems, the present inventors have conducted extensive studies on a method of cleaning an organic compound which has adhered to the inner surface of a chamber of a deposition apparatus or to the surface of components disposed in the chamber, with an organic solvent, and recovering the organic compound.
To carry out the above method, it is considered to be necessary to carry out cleaning by using an organic solvent which provides a solubility of the above organic compound to a certain extent. However, an organic solvent in which a compound generally used as a material for production of an organic EL device is soluble is limited.
For example, as the above organic compound, aluminum tris(8-hydroxyquinolinate) (hereinafter referred to as Alq3) may be mentioned. As an organic solvent in which Alq3 is soluble, chloroform has been known. However, a hydrochlorocarbon such as chloroform has high ozone depletion potential.
It is an object of the present invention to provide a method for cleaning a chamber of a deposition apparatus for organic EL device production, which reduces the production cost by recycling a material accumulated on the inner surface of the chamber at the time of organic EL device production and wasted, which prevents inclusion of the material accumulated on the inner surface of the chamber as an impurity in a thin film as a product, and which is free from environmental problems such as ozone depletion.